Design of Servo Control System with Linear Motor Based on Digital Filter Technology
|School||Harbin Institute of Technology|
|Course||Instrument Science and Technology|
|Keywords||linear motor fixed frequency noise IIR digital notch filter zero-phase filter|
Laser Direct Writing (LDW) is an advanced fabrication equipment of diffractive optical elements (DOE), its fabrication precision determines the quality of imaging. With the fast advancement of the optics technology, the research of LDW will be significant in the future, simultaneously advancing the development of ultra-precision fabrication technology. Position control system is the important part of LDW, the performance of which effects LDW greatly, because the precision of position control system is relative to the precision of writing precision of LDW. This paper aiming at the restraint and attenuation of control system noise, mainly researches digital filter technology based on servo control system composed of linear motor and air-bearing slider stage. At the same time, this paper also designs the hardware of each part in control system.This paper analyzes the constitute of linear motor servo control system first, then aquires the spectrums energy distributing of linear motor’s following errors using experiment means, accordingly to fix the noise frequency of the control system. To eliminate negative effection brought by fixed frequency, this design adds a digital filter to controller tache and choses a digital notch to filter the interfere signal considering the control system.To keep the steep character of notch filter implemented by FPGA, this paper choses the model of 2-order IIR notch filter based on all-pass filter to design the coefficients according to the frequency of noise. Moreover, elicited by zero-phase filter, this paper puts forward a method to design a real-time IIR notch filter based on zero-phase filter, the simulation result indicates that this method makes the phase character of IIR filter to be linear and the beginning part of signals are not distorted.This paper also designs the control system hardware circuits which include signal transform circuit, fourfold pulses module, speed and position measure module of linear motor and IIR notch filter module. Thereinto, this paper mostly discusses the implement means of filter with FPGA including calculation timing analyse of filter, the choice of gain coefficient and structure optimum aspects. The result of module simulation confirms that the IIR digital notch filter is effective.At last, this paper tests the servo control system based on linear motor in chapter 5. Through analyzing the datum of the position errors, it is illuminated that IIR notch filter can restrain the noise frequency effectively and advance the position precision at a certain extent.